Sol-gel processing of ZrO2 is performed via hydrolytic polycondensation of zirconium tetrapropoxide Zr(OPr)4 in the presence of acetic acid. The gelation times as well as the aspects of the produced gels are studied as functions of the molecular ratios h = H2O/ Zr(OPr)4 and k = CH3COOH/ Zr(OPr)4. I.R. study shows that molecular precursors of general formula Zr(OPr)x (AC)y are formed in which the bidentate acetates (Ac) replace the OPr groups and are directly bounded to zirconium by both chelation and bridging. Ac ligands exhibit a strong resistance to the action of water and their departure by heating is only possible at temperatures higher than 200°C. Water, indispensable for hydrolysis of Zr(OPr)x (Ac) species, is formed in-situ by action of acetic acid on n-PrOH. Further addition of water isn't necessary.
C. Ben Amara, N. Gharbi, H. Zarrouk